var VS_SHADER_RESOURCE = 
    "uniform mat4 u_RotateMat;\n"+
    "attribute vec4 a_Position;\n"+
    "attribute vec4 a_Color;\n"+
    "varying vec4 v_Color;\n"+
    "void main(){\n"+
    "   v_Color = a_Color;\n"+
    "   gl_Position = u_RotateMat * a_Position;\n"+
    "}\n";
var FS_SHADER_RESOURCE = 
    "precision mediump float;\n"+
    "varying vec4 v_Color;\n"+
    "void main(){\n"+
    "   gl_FragColor = v_Color;\n"+
    "}\n";

function main() {
    var canvas = document.getElementById("canvas_id");
    gl = getWebGLContext(canvas);
    if(! gl){
        console.error("not find gl!!!");
        return
    }
    if(!initShaders(gl, VS_SHADER_RESOURCE, FS_SHADER_RESOURCE)){
        console.error("init shader fail!!!");
        return
    }
    var n = initShaderBuffer(gl);
    if(n > 0){
        curTime = Date.now();
        tick();
    }
}


var rotaMat;
var curTime;
var u_rotateMat;
var gl;
var angle = 0;
var a_Color;
function initShaderBuffer(gl){
    rotaMat = new Matrix4();
    var buffer = gl.createBuffer();
    if(! buffer){
        console.error("init cache buffer fail !!");
        return -1;
    }
    var a_Position = gl.getAttribLocation(gl.program, "a_Position");
    u_rotateMat = gl.getUniformLocation(gl.program, "u_RotateMat");
    a_Color = gl.getAttribLocation(gl.program, "a_Color");
    // gl.uniform4f(u_color, 1.0,0.0,0.0,1.0);
    var pointArr = new Float32Array(
        [
            0.2,0.5,
            0.0,0.2,
            0.5,0.5
        ]
    );
    gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
    gl.bufferData(gl.ARRAY_BUFFER, pointArr, gl.STATIC_DRAW);
    gl.vertexAttribPointer(a_Position, 2, gl.FLOAT, false, 0, 0);
    gl.enableVertexAttribArray(a_Position);

    initColorBuffer(gl);
    return 3;
}


function initColorBuffer(gl) {
    var colorBuffer = gl.createBuffer();
    var colorArr = new Float32Array(
        [
            1.0,0.0,0.0,1.0,
            0.0,1.0,0.0,1.0,
            0.0,0.0,1.0,1.0,
        ]
    );
    gl.bindBuffer(gl.ARRAY_BUFFER, colorBuffer);
    gl.bufferData(gl.ARRAY_BUFFER, colorArr, gl.STATIC_DRAW);
    var ret = gl.vertexAttribPointer(a_Color, 4, gl.FLOAT, false, 0, 0);
    console.log("ret:",ret)
    gl.enableVertexAttribArray(a_Color);
}
function tick(){
    angle += getAniAngle();
    angle %= 360;
    console.log("angel:"+angle);
    draw(gl, u_rotateMat, angle, rotaMat);
    requestAnimationFrame(tick);
}

function draw(gl,u_rotateMat, angle, rotaMat){
    gl.clearColor(0.0,0.0,0.0,1.0);
    gl.clear(gl.COLOR_BUFFER_BIT);
    // rotaMat.rotate(angle, 0.0,0.0,1.0);
    rotaMat.setRotate(angle, 0.0,0.0,1.0);
    gl.uniformMatrix4fv(u_rotateMat, false,rotaMat.elements);
    gl.drawArrays(gl.TRIANGLES, 0, 3);
}

function getAniAngle() {
    var addangle = (Date.now()-curTime) / 1000 * 30;
    curTime = Date.now();
    return addangle;
}